I would go for ready made keyboard as my friends suggested but if you need to place keys in weird places like around the display or to each side you can build your own keys using high quality industry standard switches.
If you dont press more than one key at the same time (some times it is necessary like if you want to go in debug mode you press 3 switches at same time) you can arrange them in a 5X8 matrix debounce and scan each row and column.
You also can connect your switches exactly as the PCs keyboard( Reverse Engineering) get the PCB of the keyboard and use it for your custom applications.
Regards
Mahmood